The father of an 8-year-old boy who was killed in the Boston Marathon bombing has told a court how he was forced to leave his dying son so he could rush his other two injured children to hospital.

William Richard was giving evidence on the second day of the trial of Dzhokar Tsarnaev, who is accused of planting bombs at the Boston Marathon on April 15 2013.

Of the three people killed in the attack, Mr Richard’s son, Martin, was the youngest. 264 people were also injured.

“I saw a little boy who had his body severely damaged by an explosion and I just knew from what I saw that there was no chance,” he told the court.

Witnesses were recounting the final moments of the three people killed in the blasts.

One Boston city police officer says he remembers administering CPR to a 29-year-old Krystle Campbell, another of those killed in the attacks.

Another officer recounted how she was urged by her captain to abandon the body of 23-year-old Lingzi Lu over fears there could be another bomb targeting aid and response teams.

Mr Tsarnaev, who is 21, has admitted that he and his brother planted the two bombs, but is pleading not guilty.

He is also charged with in fatal shooting of a police officer three days later during a manhunt. His elder brother Tamerlan was killed during the shootout.

Mr Richard recounted loading his eldest son, Henry, and his young daughter, Jane, then 5, into an ambulance.

He said he saw how badly injured Martin was and realised that he would not survive.

“I knew in my head that I needed to act quickly or we might not only lose Martin, but we might lose Jane too,” he told the court.

The witness’s wife, Denise, who had been blinded by the blast, stayed with the 8-year-old in his final moments.

Richard accompanied the other two children to hospital; his daughter Jane lost a leg in the blast.

In 2013 the BBC’s Panorama programme revealed that one of the brothers who carried out the attack read far-right American literature shortly before he carried out the massacre.

Tamerlan Tsarnaev was understood to have read articles that argued 9/11 and the 1995 Oklahoma City bombings were government conspiracies, along with an article on "the rape of our gun rights".

Other alleged motives for the attack include Chechen separatism and radical Islamist views.

In August 2013 the US magazine Rolling Stone put Dzhokhar Tsarnaev on its front cover with the headline: “The Bomber: How a popular, promising student was failed by his family, fell into radical Islam and became a monster”. The edition was boycotted by some retailers.